Electropolishing apparatus



Nov. 13, 1962 c. A. JOHNSON 3,053,928

ELECTROPOLISHING APPARATUS Filed April 25, 1960 2 Sheets-Sheet 1 o o o o o o 16 l0 H L L @@(PN) 1- s f3 ul un In V:lll la m' Fiqul.

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ELECTROPOLISHING APPARATUS Filed April 25, 1960 2 sheets-sheet 2 rllllllll' r l.

IN VEN TOR.

Comm y A. Jomvsou grroleA/EVS United States Patent O 3,063,928 ELECTROPOLISHING APPARATUS Conway A. `lohnson, Detroit, Mich., assignor to Automotive Rubber Co., Inc., Detroit, Mich., a corporation of Michigan Filed Apr. 25, 1960, Ser. No. 24,451 8 Claims. (Cl. 204-206) This invention relates to the electropolishing of metal strips and particularly to the electropolishing of stainless steel.

It is well-known to electropolish a metal strip by moving the strip through an acidic bath and having an electric current pass through 4the bath with an electrode submerged in the bath and the strip forming an electrode of opposite polarity. In such apparatus, it is customary to use wood supports or blocks to prevent the metal strips from coming into contact with the electrodes in order to preclude the possibility of causing a burning of the metal strip by contact with the electrode. Such wood blocks are subject to deterioration in the acidic bath and therefore produce splinters which often become deposited on the metal strip and generally provide an unclean and' unsightly appearance of the bath. In addition, it is necessary in the manufacture of the electrode structures which are submerged in the bath to eliminate welds as much as possible because welds tend to cause a carbon precipitation in the bath. An additional problem that has been present in electropolishing apparatus is the control of the current density in the bath.

It is an object of this invention to provide an electropolishing apparatus wherein the use of wood blocks and similar additional supports which are subject to deterioration is completely eliminated.

It is a further object of the invention to provide such an electropolishing apparatus including an electrode construction wherein only the effective portions of the electrode are made of high-grade, high-cost material while other portions which serve only as conductors are made of a lower cost material.

It is a further object of the invention to provide an electropolishing apparatus wherein control of the current density is obtained thereby obviating the stray cur-rents that are usually present in such apparatus.

Basically, the invention comprises a pair of spaced generally vertical plates which are submerged in the bath and have portions thereof extending upwardly above the bath and two sets `of transverse rods, between which the metal strip passes, extending between and xed to said plates. The portions of the plates which are submerged in the bath and the entire areas of the rods adjacent the metal strip are coated with a layer of insulating material except for isolated areas which are exposed to permit the current to pass between the electrodes and the metal plates. These areas are so spaced and arranged that even if the metal strips move into contact with the electrodes, a layer of insulating material prevents direct metal to metal contact and thereby eliminate the burning of the metal strip.

In the drawings:

FIG. l is a perspective View of the portion of the electropolishing apparatus embodying the invention.

FIG. 2 is a sectional view taken along the line 2--2 in FIG. 1.

FIG. 3 is a front elevational view of the apparatus shown in FIG. l.

FIG. 4 is a side elevation of the view of the apparatus.

FIG. 5 is a fragmentary sectional view taken along the line 5-5 in FIG. 4.

FIG. 6 is a fragmentary sectional view taken along the line 6-6 in FIG. 3.

As shown in FIG. l, the electropolishing apparatus embodying the invention is directed particularly to the electrodes that are submerged in the bath. Specifically, the apparatus comprises a pair of spaced plates 10 which are generally vertical and are made of a conductive material. Plates 10 include portions 11 which are adapted to extend upwardly above the level of the bath. A first set 12 of rods are lixed at right angles between plates 10 and extend transversely to the longitudinal movement of Ithe metal strip s through the bath and in overlying relationship to the strip s. A second set 13 of rods of conductive material are iixed at right angles between plates 1.0 transversely of the path of movement of the strip s and beneath the strip s. Each rod of sets 12, 13 is made of a conductive material which is suitable for the rod to act as the electrode in the electropolishing apparatus. Each rod is of identical construction and is fixed at its end to the plates by extending through an opening 14 in the plates 10 and is welded thereto as by welds 15.

The entire submerged surface of the plates 16 and the entire area of the rods in each set 12, 13 of rods is coated with a layer L of electrically insulating material except for exposed longitudinally spaced areas of the rods adjacent the metal strip. Specifically, as shown in FIG. 3 the endmost rods 16 are coated with a layer of electrically insulating material L except at areas 17 which are semicircular in transverse extent and are spaced longitudinally along the length of the rods 16. Similarly, rods 18 intermediate the endmost rods 16 are coated with a layer L of electrically insulating material except for exposed areas 19 which are semicircular in transverse extent and are spaced longitudinally along the length of the rod.

The areas 17 of the endmost rods are smaller in longitudinal extent so that in the event that the metal strip tends to sag downwardly or move upwardly into contact with the endmost electrodes, direct metal to metal contact is prevented by the portions of the layer L between the areas 17. The areas 19 on the intermediate rods 13 are spaced apart a greater distance since there is no danger of the metal strip coming into or bending into contact therewith and the extent of the portions of the layer L between the areas 19 is sulicient to prevent downward or upward movement of the metal strip and to metal into metal electrical contact.

By varying the extent of the exposed areas 19 and 17, it is possible to obtain a controlled current density between the electrodes and the metal strip s.

The layer L of electrically insulating material may be applied by molding or by dipping. In the latter case, the,

exposed areas 17, 19 are formed after dipping by stripping and cutting selected portions of the layer away from the rods. The electrically insulating material may comprise by the acid bath of the electropolishing apparatus. In addition, the electrical insulating material should not be adversely alected by any heat involved in the electropolishing apparatus.

The provision of the exposed areas only adjacent the surface of the metal strip s prevents the creation of stray currents which would adversely aiect the construction on the tank. Obviously, the electroplating apparatus embodying the invention eliminates the need of any wood blocks or supports together with the inherent disadvantage of such supports.

Finally, since the entire submerged area of the plates 10 is coated with a layer of insulating material and the connection between the plates and the electrodes is also coated with a layer of insulating material, the plates may be made of a material that is conductive but not neces- -sarily of the type which is required for the rod or electrode. Thus, in the polishing of stainless steel, the plates 1l) may be made of a mild steel while the rods are made of an electrode material such as stainless steel. Obviously, this results in substantial savings in cost of the apparatus.

A further advantage of the electropolishing apparatus made in accordance with this invention is that straight current is prevented from decomposing the carbon brick lining which is normally used to protect the acid-resistant membrane, which is a layer of plastic or rubber underneath the carbon brick, from physical damage and excessive heat temperature adjacent the bottom and ends of the electrodes.

I claim:

1. In an apparatus for electropolishing a metal strip by moving the strip continuously through an acid bath containing an electrode with the strip comprising an electrode of opposite polarity, the improvement comprising a pair of spaced generally vertical plates of conductive material submerged in said bath with portions thereof extending above said bath, transverse rods of conductive material fixed to said plate and extending between the plates, said rods being positioned in such a manner that the metal strip passes between certain of said rods, the submerged portions of said plates and the entire areas of said rods being coated with a layer of electrically insulating material except for areas longitudinally spaced from each said rod which are exposed adjacent the metal strip only.

2. The combination set forth in claim l wherein said exposed areas are semicircular in transverse extent.

3. In an apparatus for electropolishing a metal strip by moving the strip continuously through an acid bath in a tank containing anelectrode with the strip comprising an electrode of opposite polarity, the improvement comprising a pair of transversely spaced generally Vertical plates of conductive material submerged in said tank with portions thereof extending upwardly above the bath, a first set of rods of conductive material extending transversely between said plates and overlying the path of movement of the metal strips, said rods being spaced longitudinally of the path of movement, a second set of rods extending transversely between said plates beneath said first set of rods and beneath the path of movement of the metal strips, each set of said rods lying in a substantially common plane, said second set of rods being spaced longitudinallyv of the path of movement, the submerged portions of said plates and the entire areas of said rods being coated with a layer of electrical insulating material except for areas spaced longitudinally of the rods which are exposed adjacent the metal strip only, each said exposed area being generally semicircular in transverse extent.

4. The combination'set forth in claim 3 wherein said rods are made of stainless steel.

5. The combination set forth in claim 3 wherein the exposed areas of the longitudinally endmost rods have a lesser extent along the length of the rods than the exposed areas of the rods intermediate the endmost rods in each set of rods.

6. In an apparatus for electropolishing a metal strip by moving the strip continuously through an acid bath containing an electrode with the strip comprising an electrode of opposite polarity, the improvement comprising a pair of spaced generally vertical plates of mild steel submerged in said bath with portions thereof extending above said bath, transverse cylindrical rods of stainless steel fixed to said plate and extending between the plates, said rods being positioned in such a manner lthat the metal strip passes between certain of said rods, the submerged portions of said plates and the entire areas of said rods being coated with a layer of electrically insulating ma- -terial except for areas longitudinally spaced from each said rod which are exposed adjacent the metal strip only.

7. In an apparatus for electropolishing a metal strip by moving the strip continuously through an acid bath in a tank containing an electrode with the strip comprising an electrode of opposite polarity, the improvement comprising a pair of transversely spaced generally vertical plates of conductive material submerged in said tank with portions thereof extending upwardly above the bath, a first set of cylindrical rods of conductive material extending transversely between said plates and overlying the path of movement of the metal strip, said rods being spaced longitudinally of the path of movement, a second set of cylindrical rods extending transversely between said plates beneath said first set of rods and beneath the path ofv movement of the, metal strip, each set of said rods lying in a substantially common plane, said' second set of rods being spaced longitudinally of the path of movement, and welded portions connecting the ends of said rods to said plates, the submerged'. portions of said plates, the welded portions, and the entire areas of said rods being coated with a layer of electrical insulating material except for areas spaced longitudinally of the rods which are exposed adjacent the metal strip only, each said exposed area being generally semicircular in transverse extent.

8. In an apparatus for electropolishing a metal strip by moving the strip continuously through an acid bath containing an electrode withA the strip comprising an electrode of opposite polarity, the improvement comprising a pair of spaced generally vertical plates of mild steel submerged in said bath with portions thereof extending above said bath, an upper and lower set, transverse cy V'lindrical rods of stainless steel welded to said plate and extending between the plates, each set of said rods. lying in a single plane, said rods being positioned in such a manner that the metal strip passes between said sets of said rods, the submerged portions of said plates and the entire arcas of said rods being coated with a layer of electrically insulating material except for areas longitudinally spaced from each said rod which are exposed adjacent the. metal strip only.

References Cited in the file of this patent UNITED STATES PATENTS 915,846 Freidheim Mar. 23, 1909 2,395,437 verraste ?-T Feb. 26, 1946 

1. IN AN APPARATUS FOR ELECTROPOLISHING A METAL STRIP BY MOVING THE STRIP CONTINUOUSLY THROUGH AN ACID BATH CONTAINING AN ELECTRODE WITH THE STRIP COMPRISING AN ELECTRODE OF OPPOSITE POLARITY, THE IMPROVEMENT COMPRISING A PAIR OF SPACED FENERALLY VERTICAL PLATES OF CONDUCTIVE MATERIAL SUBMERGED IN SAID BATH WITH PORTIONS THEREOF EXTENDING ABOVE SAID BATH, TRANSVERSE RODS OF CONDUCTIVE MATERIAL FIXED TO SAID PLATE AND EXTENDING BETWEEN THE PLATES, SAID RODS BEING POSITIONED IN SUCH A MANNER THAT THE METAL STRIP PASSES BETWEEN CERTAIN OF SAID RODS, THE SUBMERGED PORTIONS OF SAID PLATES AND THE ENTIRE AREAS OF SAID RODS 